Computerized object recognition is useful in many fields. For example, in a forward terrain display based on infrared imaging for night flying, it is important to display accurate outlines of obstacles such as hills against a cluttered background; or in the automatic recognition of an unknown object by comparing its shape to known reference object shapes, it is important that the outline of the unknown object be accurately determined.
In prior art techniques such as that described in the article entitled "Dynamic Occlusion Analysis in Optical Flow Fields" by W. B. Thompson and K. M. Mutch, IEEE Transactions on Pattern Analysis and Machine Intelligence, vol. 7, pp. 374-383 (1985), range discontinuities in a scene are determined by locating image areas in which the range of image components changes abruptly. A problem with this approach is that in order to determine the range of an image component, the component must be identifiable (as, e.g., by the presence of an intensity transition or edge) in each of two images of the scene taken from slightly different locations (referred herein as pairs of stereoscopically related images), so that its range can be computed from its relative displacement between, and location, in the two images. As a result, range information in cluttered, noisy or indistinct images is available for only a relatively small number of pixels in a given scene. The range of the remaining pixels must be determined by interpolation--a problem which is further complicated by any noise spikes appearing in the image.
Because of this interpolation, which inherently reduces the sharpness of transitions, locating range discontinuities is difficult and potentially inaccurate. It is therefore desirable to provide a method of locating range discontinuities which is more accurate and reliable.
Besides the article mentioned above, the prior art includes the following references:
Gerharz U.S. Pat. No. 3,961,851 which relates to the synchronized control of multiple cameras for the purpose of passive ranging by a human operator; Beckwith et al. U.S. Pat. No. 4,489,389 which relates to a perspective map display but does not involve any ranging; Grumet U.S. Pat. No. 4,601,053 which measures range by using side-by-side TV cameras but does not deal with range discontinuity detection; Merchant U.S. Pat. No. 4,635,203 which computes range information for each point in a scene but tends to smooth out discontinuities rather than sharpen them because it fails to prohibit interpolation across segmentation boundaries; and Merchant "Exact Area Registration of Different Views of a Common Object Scene", Optical Engineering, May/June 1981, Vol. 20, No. 3, pp. 424-436, which deals with a transformation algorithm for providing exact area registration in a scene but is not concerned with range discontinuity detection.